Scanning device

ABSTRACT

A device suitable for use as a scanning directional radio receiver or transmitter.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to a co-pending U.S. patent applicationSer. No. 15/615,103 filed Jun. 6, 2018 entitled “Scanning Device”, whichin turn claims priority to U.S. Provisional Patent Applications Ser. No.62/346,757 filed Jun. 7, 2016 entitled “Flat Optical Camera”, and Ser.No. 62/346,779 filed Jun. 7, 2016 entitled “Flat Coherent SolarConcentrator”, and Ser. No. 62/454,393 filed Feb. 3, 2017 entitled“Dielectric Travelling Waveguide with Varactors to Control BeamDirection”, the entire contents of each of which are hereby incorporatedby reference.

BACKGROUND

Recent developments in the use of dielectric waveguides providefunctions normally associated with antenna arrays. The waveguides aregenerally configured as an elongated slab with a top surface, a bottomsurface, a feed end, and a load end. The slab may be formed from two ormore dielectric material layers such as silicon nitride, silicondioxide, magnesium fluoride, titanium dioxide or other materialssuitable for propagation at a desired frequency or wavelength ofoperation.

In one implementation, physical gaps are formed between the layers. Acontrol element is also provided to adjust a size of the gaps. Thecontrol element may, for example, be a piezoelectric or electroactivematerial or a mechanical position control. Changing the size of theadjustable gaps has the effect of changing the effective propagationconstant of the waveguide. This in turn allows for scanning theresulting beam at different angles. These devices have been designed foruse at radio frequencies, acting as a directional radio antenna, and atvisible wavelengths, acting as a solar energy concentrator.

See U.S. Pat. Nos. 8,582,935, 8,710,360 and 9,246,230, incorporated byreference herein, for some example implementations.

As explained in those patents, a coupling layer may also be used thathas a dielectric constant that changes as a function of distance fromthe excitation end to the load end. By providing increased couplingbetween the waveguide and the correction layer in this way, horizontaland vertical mode propagation velocities may be controlled.

Adjacent dielectric layers may be formed of materials with differentpropagation constants. In those implementations, layers of lowdielectric constant material may be alternated with layers of highdielectric constant material. These configurations can providefrequency-independent control over beam shape and beam angle.

The waveguide may also act as a feed for a line array of antennaelements. In is some implementations, a pair of waveguides are used.Coupling between the variable dielectric waveguide(s) and the antennaelements can also be individually controlled to provide accurate phasingof each antenna element. See for example U.S. Pat. No. 9,509,056incorporated by reference herein.

The elements of an antenna array may also be fed in series by astructure formed from a transmission line disposed adjacent a waveguidewith reconfigurable gaps between layers. The transmission line may be alow-dispersing microstrip, stripline, slotline, coplanar waveguide, orany other quasi-TEM or TEM transmission line structure. The gapsintroduced in between the dielectric layers provide certain properties,such as a variable propagation constant to control the scanning of thearray.

Alternatively, a piezoelectric or ElectroActive Polymer (EAP) actuatormaterial may provide or control the gaps between layers, allowing theselayers to expand, or causing a gel, air, gas, or other material tocompress. See U.S. patent application Ser. No. 14/702,147 filed May 1,2015 incorporated by reference herein for more details.

SUMMARY

The apparatus described herein is a type of dielectric travellingwaveguide device that can be used to steer optical radiation in twodimensions. The optical device may be used as a camera or as a solarconcentrator. In a preferred implementation, the device includes a firstor main waveguide that is a generally elongated rectangle with a topsurface and exit face. A progressive delay layer is placed on the topsurface. A second or auxiliary progressive delay layer and waveguide aredisposed adjacent an exit face of the main waveguide. The delayintroduced by layers is preferably a continuous, linear propagationdelay. It may be implemented as a layer of material with a particularshape or construction as will be described below.

is For a camera implementation, optical detectors, such as onephotodiode each for the red, green, and blue wavelengths, or a broadbanddevice such as a charge coupled device (CCD), are disposed adjacent anexit face of the auxiliary waveguide.

For a solar concentrator implementation, the detector(s) may include oneor more Metal-Insulator-Metal (MIM) rectifiers. As with the cameraimplementation, the solar detector(s) may be broadband, or may beprovided by multiple narrower band detectors.

By controlling the index of refraction (c) of the waveguides and/orprogressive delay layers one can in turn scan the device by controllingan angle of incidence of energy arriving on the top face and hence onthe detector(s).

The index of refraction can be controlled by adjusting the size of a gapbetween the waveguide and delay layers. In a solid state implementation,the index of refraction may be controlled with a series of varactorsthat control the impedance of a propagation path disposed between two ormore waveguide layers.

The apparatus may be implemented with multiple substrate layers of thesame or different thicknesses. The different thickness layers may befurther arranged with a chirp or Bragg spacing to provide frequencyindependent operation.

BRIEF DESCRIPTION OF THE DRAWINGS

The following description of preferred embodiments should be readtogether with the accompanying drawings, of which:

FIG. 1 is an isometric view of one implementation of the device.

FIGS. 2A and 2B are more detailed views of the device using a wedge andgap layer.

FIG. 3 is a plot of normalized amplitude versus angle.

FIG. 4 is a similar plot to that of FIG. 3 showing cosine squaredweighting.

FIG. 5 is a plot of index of refraction versus delay for the wedge andwaveguide.

FIG. 6 is a result once these are matched.

FIG. 7A is a block diagram of one implementation using the device as acolor camera.

FIG. 7B is another implementation using the device to provide threedimensional pixel information including distance as well as imageinformation.

FIGS. 8A through 8C illustrate an alternate embodiment.

FIGS. 9A, 9B, 9C and 9D illustrate a solid-state implementation.

FIGS. 10A, 10B, 10C and 10D illustrate other solid-stateimplementations.

FIGS. 11A, 11B and 11C compare the air gap and varactor implementations.

DETAILED DESCRIPTION Scanning Device

Described herein are waveguide structures adapted for scanning in thevisible range to provide a flat optical camera, or at solar wavelengths,to provide a flat solar concentrator. Particular implementations use anauxiliary progressive delay with waveguide structure configuration tofeed a main progressive delay with waveguide structure to scan in twodimensions (2D).

FIG. 1 is a perspective view of one such implementation where a camerais provided by a main rectangular waveguide structure 11. It should beunderstood that an analogous structure can be used to provide a solarconcentrator. The waveguide 11 is a generally elongated rectangle with atop surface and exit face. Typical dielectric materials for thewaveguide may include silicon nitride, silicon dioxide, magnesiumfluoride, titanium dioxide or other materials suitable for propagationat a desired operating wavelength.

A progressive delay layer 12 is placed on the top surface. A second orauxiliary progressive delay layer 22 and waveguide 21 are disposedadjacent the exit face of the main waveguide. The delay introduced bylayers 12, 22 is preferably a continuous, linear propagation delay. Itmay be implemented as a layer of material with a particular shape or inother ways as will be described below. For the camera implementation,optical detectors 30, such as one photodiode each for the red, green,and blue wavelengths, or a broadband device such as a charge coupleddevice (CCD), are disposed adjacent an exit face of the auxiliarywaveguide 22. In the case of a solar concentrator, the detector(s) 30may include one or more MIM rectifiers. As with the cameraimplementation, the solar detector may be broadband, or may be providedby multiple narrower band detectors.

By controlling the index of refraction (c) of the waveguides 11, 21and/or progressive delay layers 12, 22 one can in turn control an angleof incidence of energy arriving on the top face and hence on thedetector(s) 30.

FIGS. 2A and 2B are a detailed side and top view of an implementation.As shown in FIG. 2A, a main structure 100 includes waveguide 101 withadjustable gaps 102 to provide an effective controllable index ofrefraction for receiving energy via the angled progressive delay layer104. One or more suitable detectors 105 (such as photodiodes in the caseof a camera implementation, or MIM diodes in the case of a solarconcentrator) are placed adjacent the waveguide.

FIGS. 2A and 2B also show the auxiliary structure 110 disposed adjacentand at an angle, such as a right angle (orthogonal to), to the mainstructure 100. A progressive delay layer is placed between a waveguide111 with adjustable gaps 112 and the output is edge of waveguide 101 inthe main structure. The auxiliary structure 110 may provide furtherdelay, in the case of a solar concentrator implementation, so thatenergy received along the main structure is coherently added “in phase”at the detector 105.

The auxiliary structure 110 provides further delay so that the energyreceived along the main structure is coherently added “in phase” at thedetector 30.

The main structure 100 provides progressive delay excitation tofacilitate scanning in the elevation direction. The auxiliary structure110 provides progressive delay excitation to effect scanning in theazimuthal direction.

The size of the gaps 102, 112 can be adjusted using piezoelectrics,electroactive or micromechanical actuators.

For implementation as a camera, the arrangement may be physically scaledand/or materials adapted to operate in a visible wavelength region fromabout 390 to 700 nanometers (0.39 to 0.70 microns). For implementationas a solar collector, the arrangement may be physically scaled and/ormaterials adapted to operate at solar wavelengths from 400 nm to 1200nm.

The resulting device can thus scan in both elevation and azimuth withoutthe need for multiple detectors, or mechanical scanning apparatus toprovide a “flat” camera suitable for packaging in a smartphone, tablet,laptop, portable computer, or other handheld device.

However, a solar collector implementation may also be mounted onmechanical scanning and/or sun tracking apparatus. That apparatus maymake of MEMS actuators to track the sun. The result in any event is arelatively “flat” concentrator of solar energy making it quite suitablefor packaging. Multiple devices can be fabricated on a singlesemiconductor wafer; the wafers in turn can be packaged in a flat solarpanel.

Camera Image Quality and Telephoto Mode

For a camera implementation, the resulting scanning phased array makespossible a camera capable of functioning in a high resolution telephotolens configuration. Consider both objects at 1000 feet and objectscloser to the camera. For example, to recognize a face at 1000 feet aphased array structure 100 of one inch in size will result in a pixelsize of 0.36 inches. Coverage over a field of view (FOV) of 90 degreesmay thus produce the equivalent of 40 million pixels. For a one inchdiameter the far field starts at 1000 feet, while the Fresnel regionbegins at 1000 feet.

FIG. 3 is taken from Shackelford, Robert G., “Fresnel Zone RadiationPatterns of Microwave Antennas”, Georgia Institute of Technology, M. S.Thesis, 1962, shows the shape of a beam of a 5000 wavelength aperturewith a reduced field of view, that is, from the start of the far fieldregion to ⅛ of the distance to the far field. The far field beam patternshould be similar to the 1000 foot pattern for the one inch diameteroptical phased array, while the ⅛ factor should be indicative of thepattern at 125 feet.

FIG. 4, also from Shackelford, shows the patterns with a cosine squaredweighted aperture. All the beam shapes are close to the shape for thefar field case, showing that for both nearby and far field objects, goodquality images will be formed.

In other words, unlike a conventional digital camera that use largearrays of individual CCD detectors, the resulting image resolution isindependent of the number of detectors. Indeed, even a single, highspeed detector may now be used with the scanning array. By controllingthe field of view, the scanning device can be used to provide atelephoto, binocular and/or microscope operating modes without loss ofresolution. Because only a single detector is required, it may be arelatively expensive detector to provide other features, such asrelatively high sensitivity to low light.

Correction for Dispersion

The beam direction in a continuous waveguide with a progressive delaylayer (such as for the structures described in FIGS. 2A and 2B) isaffected by dispersion in the waveguide and the progressive delay layer.Rather than eliminating the dispersion for each component, it ispossible to match the dispersions in the waveguide and progressive delaylayer. The beam direction in this case is

cos (theta)=β(waveguide)/β(progressive delay layer)

where β is the propagation constant. Using data for the index ofrefraction of titanium dioxide in the optical range, example waveguideand the progressive delay layer dispersions are seen in FIG. 5. Each ofthe waveguide/progressive delay layer pairs of FIGS. 2A and 2B combinethese dispersions resulting in a relatively constant effect on the beamdirection over a range of wavelengths. See FIG. 6, showing anapproximate one (1) degree error resulting in the scan angle, theta.

Scanning the Red, Green and Blue (RGB) Bands

It is possible, in some camera implementations, to include a photodiodeor CCD for all of the RGB bands and thus to detect three colorssimultaneously.

However, to compensate for dispersion and subsequent loss of angularresolution, it is also possible to scan the RGB bands separately. In theexample shown in FIG. 7A, a single optical output of the array 100 ofFIGS. 2A and 2B (or of FIGS. 9A, 9B, 9C, or 10A) is split to feed a setof RGB filters 770 and RGB photo diodes 780. One of the image outputs(such as the G band image) is then used as a calibrated beam scan.Alignment of is the RGB images is then accomplished by using a patternrecognizer 790 with the G image is used as a template. For example, apattern recognizer may note an autocorrelation peak location of G. R andB are then cross correlated with the G image. The R and B peak locationsrelative to the G autocorrelation peak location may then be used tospatially align the R and B images with the G image; the RGB images arethen summed to provide a composite image.

Timing circuitry (not shown), as is known, may then synchronize, sample,and digitize the resulting composite and/or separate RGB signals toprovide a digital image to an output device such as a touch sensitivedisplay 795 in a smartphone.

Another implementation is to stack the RGB diode detectors 780 in avertical array that Red is first detector, Green is the next and Blue isthe last in the stack. This allows the Green and Blue to pass throughthe Red and the Blue to pass through the Green.

To improve the signal to noise ratio (SNR) it is possible for the diodes780 to dwell on the pixel of interest for a longer period of time.Another approach to improve SNR is to utilize a detector that has aninherently better SNR.

Meta Material Flat Progressive Delay Layer

If the optical camera must be truly as flat as possible, the progressivedelay layer 12, 22 may be replaced with an equivalent engineeredmaterial structure. In this implementation, as shown in FIGS. 8A, 8B and8C, circular cross section titanium dioxide nano pillars 800 may be usedas resonant structures where the delay through the pillar is related tothe diameter. It may be possible to combine multiple juxtaposed resonantpillars, each resonant at the Red (R), Green (G) and Blue (B) wavelengthregion to achieve the required RGB bandwidth. There may be one or morepillars 800 resonant in is each of the R, G, B wavelengths.

Solid State Implementations

It is also possible to use fixed, solid state structures to achieve thesame effect as the adjustable gaps described above. Theseimplementations may be preferred as they enable scanning the devicewithout the need for an angled layer or actuators to control the gapspacing.

FIG. 9A is an isometric view of an implementation of the main waveguide100 of the device using this approach. It should be understood that theauxiliary waveguide 110 placed adjacent the exit face of waveguide 100may be similarly constructed, with detector(s) 105 placed adjacent theexit face of the auxiliary waveguide, as in the embodiment of FIGS. 2Aand 2B.

Here, waveguide 100 (or waveguide 110) includes an upper waveguide layer910, middle layer 920, and lower waveguide layer 930. Middle layer 920,also called the varactor layer herein, is formed of alternating sections925, 40 of different materials having different respective dielectricpropagation constants. An example first section 940 is formed of a firstdielectric material having the same, or nearly the same, propagationconstant as layers 910, 930. An example second section 925 is formed ofa second dielectric having a different propagation constant than thefirst section 940.

As shown in FIG. 9B and 9C, layers 910, 130 and sections 940 may have afirst propagation constant ϵ₁, and sections 125 may have a secondpropagation constant of ϵ₂. In one implementation, ϵ₁ is 36 and ϵ₂ is 2;that is, ϵ₁ is much greater than ϵ₂.

A material such as Indium Titantium Oxide (ITO) may be deposited on thetop and bottom of sections 940 such as at 941, 942 to provide avaractor. A control circuit is (not shown) imposes a controllablevoltage difference, V, on 941, 942. It should also be understood thatconductive traces are deposited on one or more of the layers toconnected the varactors to a control circuit (also not shown).

The control voltage applied to the varactor thus changes the impedanceof paths, P₁, from the upper waveguide 910, through the dielectricsection(s) 940 to the lower waveguide 130. When that control voltage, V,is relatively high, the dielectric sections 940 become more connected tothe adjacent layers 910, 930—that is, the impedance through path P₁ isrelatively lower than the impedance through paths P₂. When that voltagedifference is relatively smaller, the impedance through path P₁ becomesrelatively higher.

Changing the voltage V thus changes the overall propagation constant ofthe waveguide 100. The voltage V can thus be used to steer the resultingbeam.

In some implementations, there may be further control over the voltagesapplied to different ones of the sections 940 to provide a differentimpedance of the waveguide structure as a function of horizontaldistance. That approach can provide the same properties as the wedge ortaper layers in the implementation of FIGS. 2A and 2B above.

For example, if the impedance through path P₁ is given by z₁ and theimpedance through path P₁ by z₂, and those impedances are progressivelychanged as a function of distance, x, along the waveguide, the relativepropagation constant βO can be shown to be a function of z as follows:

$\beta_{o} = \sqrt{\frac{z\; 1}{z2}}$

with the impedance, z, of a particular varactor section 940 may dependupon a ratio of its width and height.

To provide progressive delay along the waveguide, the impedance z of aparticular waveguide section may be changed as a function of itsposition or distance, x, along the waveguide, such that z₁=z₁(x) andz₂=z₂(x). In this way, one can effect a delay to incident energyarriving at the waveguide depending upon location along the waveguide.This provides the analogous result as the implementation of FIGS. 2A and2B that use wedge shaped layers 104, 114.

One can also control the amount of dispersion in the waveguide 100 bycontrolling the spacing F between the varactor sections 940. Spacingthem at a fraction of the operating wavelength (λ) of about λ/10 apartappears to be preferable, although λ/4 would provide more dispersion.

FIG. 9D illustrates an implementation with more than three layers. Herethe layers 910, 920 and 930 may have progressively larger thickness,although implementations with multiple layers 910, 920 and 930 withuniform thickness is also possible. The relative increase in thicknesscan follow a proscribed pattern, such as a chirped or Bragg pattern, asdescribed in the patents and patent applications referenced above.

The scanning main with scanning auxiliary waveguide 100 and 110structure can be used with radio frequency (RF) antenna arrays ofdifferent types. For example, waveguide 100 may be used to feed one ofthe Orientation Independent Antennas described in U.S. Pat. Nos.8,988,303 and 9,013,360 as well as U.S. patent application Ser. No.15/362,988 filed Nov. 29, 2016 all of which are hereby incorporated byreference.

In another solid state implementation, shown in FIGS. 10A (side view)and FIG. 10B (top view), the waveguide is formed of two facing layers ofa material such as zinc oxide (ZnO). A magnesium fluoride (MgF₂) layeris formed on each facing surface such as by sputter deposition on thetwo facing ZnO layers. Conductive fingers are deposited on the facingsurfaces to form interdigital transducers. By driving the twotransducers with opposite phases (+and − sine waves, for example at 1GHz), a standing acoustic wave may be produced along the facing surfacesas shown. Changing the frequency of the driving signal then changes thepropagation constant of the waveguide.

Another solid state implementation is shown in FIG. 10D. There theprogressive delay continuous phase structure is similar to that of FIG.10A, but fed with a pair of opposite phase chirp signals instead ofopposing sinusoids. The specific delay in the structure of FIG. 10Dshould be greater as one moves from right to left (away from thelocation of the interdigital transducers). Preferably, one would use afixed chirp, while the solid state structure below would be used tochange the propagation constant to change the beam direction.

Distance Detection

The same array shown in FIGS. 1, 2A and 2B (or FIG. 9 or FIG. 10, etc)may be used as a lightwave based distance detector (Lidar) when operatedin the “transmit” direction. In this implementation, a light source suchas a laser is placed adjacent where the detectors 30 are shown inFIG. 1. With the light source activated, the array 10 then provides asteerable light beam exiting from the top face 31. Known pulse rangingtechniques may then be used (for example, a light pulse can be emitted,and the time of receipt of a reflection detected) to provide a rangingfunction.

As a result, the device can be operated in two modes, the 2D “cameramode” as described above during a first time period, and then the Lidarranging mode during a second time period. The resulting outputs can becombined to associate a distance with io each pixel and thus to producea 3D image. This 3D image can be applied to create a virtual oraugmented reality image. The device thus eliminates complicatedgraphical algorithmic processing that would otherwise be necessary todetermine the position of objects in 3D space. As shown in FIG. 7B, thedevice 100 may thus be packaged in a smartphone 700 along with a controlcircuit 720 that alternately operates the device 100 is in the cameramode (to capture image data) and the Lidar mode (to capture distanceinformation), to output 3D pixels. The control circuit may include imageand distance data buffers. The 3D pixel data may then be fed to aprocessor 730 that is executing an augmented reality application program740.

In other implementations, it may be possible for the control 720 tooperate one-half of the array in the 2D camera mode, and the otherone-half of the array in the Lidar mode simultaneously.

Two other approaches to provide distance detection are (a) to use twoflat optical cameras to provide parallax allowing for the calculation ofdistance or (b) using a shutter on the camera to allow half of thecamera to collect a first image and then move the shutter to the otherhalf of the camera and collect a second image.

Micro-Illumination

Since the system is reciprocal, it can illuminate the image of interestwith a laser source that will provide illumination for the pixel that isbeing imaged. By inserting a laser source at the detector location it ispossible to transmit to the pixel location of interest.

Comparison of Air Gap and Solid State Implementations

FIGS. 11A through 11C compare the operation of the air gapimplementation of FIGS. 2A and 2B with varactor implementation of FIGS.9A, 9B and 9C. FIG. 11A is the result of a computer simulation showingrelative epsilon (propagation delay) versus air gap size. Thisparticular simulation was for a radio frequency implementation operatingat four frequencies (7.25 GHz, 7.75 GHz, 7.9 GHz and 8.4 GHz). FIG. 11Bshows the is result of using the “zoom” feature at the same frequencies,but where the range of scanning angles, or field of view, has beenreduced. FIG. 11C is a similar plot for the varactor implementation,showing a similar relationship for propagation delay (for thisimplementation, versus varactor capacitance).

1. An apparatus comprising: a main waveguide structure formed as anelongated rectangle having a top surface and exit face; a mainprogressive delay layer disposed adjacent the top surface of the mainwaveguide; a second waveguide and second progressive delay layerdisposed adjacent the exit face of the main waveguide, the secondwaveguide also having a top surface and an exit face; one or moredetectors or emitters, disposed adjacent the exit face of the secondwaveguide; and wherein an index of refraction (c) of the waveguidesand/or progressive delay layers are adjustable, and wherein theprogressive delay layers are provided by a series of varactors.
 2. Theapparatus of claim 1 wherein a dispersion of the main progressive delaylayer matches a dispersion of the main progressive delay layer; and adispersion of the second progressive delay layer matches a dispersion ofthe second progressive delay layer.
 3. The apparatus of claim 1 whereinthe top face of the second waveguide structure is disposed orthogonal tothe exit face of the main waveguide structure.
 4. The apparatus of claim1 additionally comprising: a control, for progressively controlling thedelay of the main and second delay layers, thereby in turn scan an angleof incidence of energy arriving on the top face of the main waveguide intwo dimensions.
 5. A scanning apparatus comprising: a main waveguidestructure formed as an elongated rectangle having a top surface and exitface; a main progressive delay layer disposed adjacent the top surfaceof the main waveguide; a second waveguide and second progressive delaylayer disposed adjacent the exit face of the main waveguide, the secondwaveguide also having a top surface and an exit face; one or moredetectors, disposed adjacent the exit face of the second waveguide; andwherein an index of refraction (c) of the waveguides and/or progressivedelay layers are adjustable; and additionally comprising: a radiofrequency energy source or detector, coupled to the exit face of thesecond waveguide, to enable the scanning apparatus to transmit orreceive radio frequency energy.
 6. The apparatus of claim 5 wherein adispersion of the main progressive delay layer matches a dispersion ofthe main progressive delay layer; and a dispersion of the secondprogressive delay layer matches a dispersion of the second progressivedelay layer.
 7. The apparatus of claim 5 wherein the top face of thesecond waveguide structure is disposed orthogonal to the exit face ofthe main waveguide structure.
 8. The apparatus of claim 5 additionallycomprising: a control, for progressively controlling the delay of themain and second delay layers, thereby in turn scan an angle of incidenceof energy arriving on the top face of the main in two dimensions.
 9. Theapparatus of claim 5 wherein the progressive delay layers are eachprovided by a wedge layer and an adjustable gap structure.
 10. Theapparatus of claim 5 additionally comprising: a controller, foroperating the apparatus in a selected mode to produce distanceinformation.